ing."

Graham invented the "compensating mercury pendulum," the "dead
escapement," and the "orrery," none of which have been much improved
since. The clock which he made for Greenwich Observatory has been
running one hundred and fifty years, yet it needs regulating but once
in fifteen months. Tampion and Graham lie in Westminster Abbey,
because of the accuracy of their work.

To insure safety, a navigator must know how far he is from the equator,
north or south, and how far east or west of some known point, as
Greenwich, Paris, or Washington. He could be sure of this knowledge
when the sun is shining, if he could have an absolutely accurate
timekeeper; but such a thing has not yet been made. In the sixteenth
century Spain offered a prize of a thousand crowns for the discovery of
an approximately correct method of determining longitude. About two
hundred years later the English government offered 5,000 pounds for a
chronometer by which a ship six months from home could get her
longitude within sixty miles; 7,500 pounds if within forty miles;
10,000 pounds if within thirty miles; and in another clause 20,000
pounds for correctness within thirty miles, a careless repetition.

The watchmakers of the world contested for the prizes, but 1761 came,
and they had not been awarded. In that year John Harrison asked for a
test of his chronometer. In a trip of one hundred and forty-seven days
from Portsmouth to Jamaica and back, it varied less than two minutes,
and only four seconds on the outward voyage. In a round trip of one
hundred and fifty-six days to Barbadoes, the variation was only fifteen
seconds. The 20,000 pounds was paid to the man who had worked and
experimented for forty years, and whose hand was as exquisitely
delicate in its movement as the mechanism of his chronometer.

"Make me as good a hammer as you know how," said a carpenter to the
blacksmith in a New York village before the first railroad was built;
"six of us have come to work on the new church, and I've left mine at
home." "As good a one as I know how?" asked David Maydole, doubtfully,
"but perhaps you don't want to pay for as good a one as I know how to
make." "Yes, I do," said the carpenter, "I want a good hammer."

It was indeed a good hammer that he received, the best, probably, that
had ever been made. By means of a longer hole than usual, David had
wedged the handle in its place so that the head could not fly off, a
wonderful improvem